In my last blog post I showed my tests in video form, with commentary. In this post I will lay out the tests in pictures and notes.

From the last round of testing I had a few leads that I wanted to follow and try and hone in on. The search for a nice yellow glaze continued, as well as testing different tenmoku base recipes. And then I did a couple ‘shot in the dark’ tests just to see what would happen: with salt and tin oxide additions to my granite.

First up, though, let’s look at the second round of the yellow glaze search.The first picture here shows the base glazes I guessed at. Last time the glazes ran a lot. I made the mistake of using 30% dolomite as well as other materials. I was pretty sure that this was the cause of the lower than ideal melting temperatures I was seeing. So in these tests I reduced the dolomite to 20-25% and played with adding 5-10% bone ash, 10-15% zircopax, 5-15% EPK (Edgar Plastic Kaolin) and silica 5-15%.

The tests out of the gas reduction kiln were variations on a kind of peppermint green glaze. The magic happens when this glaze is soda fired. It goes yellow! The results were interesting.

In general I learnt that when you add silica, the yellowness of the glaze dissipates. John Neely said this was because it was becoming more of a proper glaze, rather than a matte glaze, undersaturated in silica. The glazes with 25% dolomite were more fluxy in a kind of mottled way. I feel like 20% is about right. In terms of zircopax, the glazes with 15% seemed yellower than 10%. This glaze also seems to be able to handle anywhere from 5-15% EPK with little color change.

Overall the winner was DP977. This may be a slightly skewed test as the atmosphere of the kiln clearly plays a big role. Test tile DP977 looks particularly toasty (reduced) so maybe this made for a warmer yellow color. We shall see in the next round! I plan on mixing up a batch of this glaze and testing it out on some actual pots. This round of tests were made with a commercial dolomite. I have collected and ground down four different local dolomites so I will also test these out in the same formula as DP 977.

The glazes with 1% iron oxide added were slightly warmer but the iron did not mix full into the tests so look dotty. At 4% added the results were not very attractive. Some of the 7% iron added tests were promising though (such as DP1022).

Here are those tests in bar form…

These tests were fired once in a gas kiln (all came out pretty bland)-I actually mistakenly put them in the gas kiln when they should have been soda fired. I think this may have skewed the results somewhat. The first three test tiles on the left were fired on the ledge by the door of the kiln so got blasted with soda. We can see from this that the soda affects the color significantly.

All of these got more soda than the small test tiles. It shows that a medium amount is necessary for the yellow color in these glazes. There were some interesting results here. DP983 is a nice warm yellow and DP988 is not bad either. This was very different from the small test tile results.

Ultimately I think quite a few of these would work as a yellow glaze. It is nice to know there is some wiggle room to adjust the glaze if need be.

In my next post I will show the results of my tenmoku attempts and the tin oxide and salt additions too.